(1) Field of the Invention
This invention relates to a method for making a multilayer coating and more particulary, to a method for the manufacture of a multilayer coating on a continuously traveling flexible support or web, which comprises simultaneously applying multiple layers of at least two nonaqueous coating liquids to form the multilayer coating on the web without interlayer diffusion or mixing of the applied layers.
(2) Description of the Prior Art
There have been known various methods for making a multilayer coating in an aqueous system, which comprise simultaneously applying multiple layers of gelatino silver halide emulsions on a support using a coating device such as of the slide hopper or extrusion hopper, cooling the applied layers with chill rolls or cold air to cause the gelation of the multilayer coating using the sol-gel transformation property of gelatin so that the viscosity of the applied layers increases to tens of thousands to hundreds of thousands of centipoises (cps) and no interlayer mixing occurs, and then drying the coating by e.g. hot air.
There have been known multilayer materials having two or more nonaqueous coatings, such as, light-sensitive materials for use in the production of printing plates using electrophotography comprising a photoconductive insulating layer and a light-sensitive layer, as described in U.S. Pat. Nos. 4,435,491 and 4,500,617 and light-sensitive materials for use in the production of printing plates comprising two or more light-sensitive layers separately provided or comprising a light-sensitive layer and an overcoat or undercoat layer, as described in Japanese Patent Public Disclosure No. 58-205154, U.S. Pat. Nos. 4,217,407 and 4,207,106, German Pat. Nos. 1,621,478 and 1,091,433, and U.S. Pat. No. 3,511,661.
Nonaqueous coating liquids have lower surface tension than aqueous coating liquids and therefore, if the former liquids are simultaneously coated and dried to form the light-sensitive and photoconductive insulating layers, or the two or more separated light-sensitive layers, or the overcoat or undercoat and the light-sensitive layers, interlayer diffusion or mixing of the coating liquids applied is liable to occur not only in the drying zone but also in the ribbon of coating composition between the coating head and the surface to be coated, or between coating and drying steps. The interlayer diffusion or mixing is accelerated because of the absence of sol-gel transformation in the nonaqueous system and therefore, it is very difficult in the nonaqueous system to form a multilayer coating in which each of the coated layers is properly separated from one another. There have not been found sol-gel transforming agents suitable for use in various nonaqueous solutions or other effective methods for making a multilayer coating in a nonaqueous system.
For this reason, multilayer coated materials, for example, light-sensitive materials for use in the production of printing plates are made by a method wherein light-sensitive and photoconductive insulating layers, or two or more light-sensitive layers are coated and dried on a hydrophilic support one after another (hereinafter referred to as the stepwise coating and drying method). The stepwise coating and drying method includes a method wherein each time a coating liquid is applied and dried on a support, the support is wound up, and a method wherein two or more coating and drying zones are provided so that two or more coating liquids are successively coated on a support and dried. The former method requires much time and expense for the production of the materials, while the latter requires very expensive equipment and high cost for the production of the materials.
There have recently been proposed several methods for making a coating on a support using electron radiation to cure the coating. For example, Japanese Patent Publication 54-19894 and Japanese Patent Public Disclosure 56-38160 disclose a method for making a single layer coating and Japanese Patent Publication 53-16403 and Japanese Patent Public Disclosure 58-24384 disclose a method for making a multilayer coating. However, this multilayer coating is made by the stepwise coating and drying method, i.e. the method wherein each time a single layer is applied, electron rays are irradiated. Thus, these methods using electron radiation do not solve the problems mentioned above.